Symptoms and control methods of diplostomiasis in fish

Main pathogens: Diplostomum spp., cercariae, metacercariae.

Affected species: silver carp, bighead carp, etc.

Optimal control period: May to August.

Identification features: diseased fish have a blackened body and are thin and weak; in the early stage of acute infection, diseased fish struggle by leaping at the water surface, or swim rapidly in the water, and when their strength is exhausted they swim slowly with the head down and tail up, losing balance, and the body may bend or there may be severe congestion around the head and eye sockets; in chronic infection, the cornea of the fish eye becomes cloudy and milky white, and in severe cases the lens falls out, resulting in blindness.

Control methods: (1) The best plan is to eradicate the first intermediate host, the pond snail, and the final host, the gull, cutting off the life cycle of Diplostomum spp. and achieving complete control. (2) Dissolve 0.5 g of copper sulfate per cubic meter of water and splash it over the whole pond, then repeat once after 1 day. (3) Mix 0.25 g of dibutyltin oxide per kilogram of fish body weight into the feed and administer for 5 consecutive days. (4) Mix 0.2-0.3 g of bithionol per kilogram of fish body weight into the feed and administer for 3-5 consecutive days. (5) Tie aquatic plants (Vallisneria is best) or terrestrial grasses into several bundles, pile them in the water around the pond in the evening to trap Diplostomum spp., then retrieve them early the next morning and dry them in the sun to kill the parasites.